I figured those masks were to keep other players from poking their fingers in to gouge eyes, noses, and mouths.
My oldest son played OL in college for several years, and he said it is an on-going thing in just about every dog-pile. One of his friends came out of a pile with a bloody eye from a defender jamming his finger in it on purpose at the bottom of a pile.
Pretty much what most players know what happens in dog-piles since pee-wee ball.
From the article:
New York Giants defensive end Justin Tuck began wearing a mask with 12 diagonal bars and five horizontal bars last summer. Tuck began wearing that mask to prevent offensive linemen from grabbing his mask and aggravating a neck strain. With Tuck dealing with a back issue during training camp, so perhaps he'll be successful in his attempt to wear it again this season.
So there are legit reasons to wear a tight pattern mask.
But, the NFL being the anal-retentive naval-gazing league it has become, will not allow any expression that might be considered individuality, and as such, uniformity is paramount for presentation of their product to maximize advertisement revenue.